Subterranean termites present a serious threat to structures, and particularly residential structures, throughout most of the United States and in many parts of the world. One of the most widely used techniques to combat termite infestation is the application of chemical agents to the ground under and around the structure. In a typical preconstruction treatment situation, a liquid form termiticide is sprayed at specified concentrations and volumes directly onto the compacted soil immediately before the concrete slab is poured, creating a horizontal barrier between any subterranean nests and the underside of the slab. Additional barriers are created in by boring holes into the soil at specified intervals (often 18 inches) or by digging trenches around the structure and spraying termiticide into the openings as well as Mixing termiticide with the backfill soil. If treatment is required to control active infestation that occurs after construction, techniques include drilling holes in infested walls and injecting liquid or powdered termiticides between the walls, boring holes in the floor slab at spaced intervals and injecting liquid termiticides into the soil, and trenching around the base of the structure and applying termiticides as in pretreatment.
In the past conventional insecticides such as the chlorinated hydrocarbons known as chlordane, DDT, aldrin, dieldrin and BHC could be effectively used to poison the soil so that transiting termites would be killed. These chemicals also remained effective in the ground for many years. Unfortunately, their effectiveness as poisoning agents extended beyond the targeted pests, and environmental concerns have resulted in prohibition of the use of any of these agents for termite treatment. Chlordane was the last such chemical available for either home or professional use, and that was banned by the United States Environmental Protection Agency in 1987.
The pest control industry has been forced to adopt a less potent class of chemical poisons for termite pre-treatment and infestation interdiction. Currently approved by the Environmental Protection Agency are chlorpyrifos (sold under the name DURSBAN TC), cypermethrin (sold as DEMON TC), fenvalerate (sold as TRIBUTE), and permethrin (sold as DRAGNET and as PRELUDE). These chemicals are generally applied in the same manner as their predecessor chlorinated hydrocarbons, namely, spraying beneath a slab or other foundation to form a horizontal barrier and injection through holes or a trench to form a vertical barrier or "curtain" through which terminates cannot penetrate without being killed. They are also used for infestation control. Unfortunately, the very characteristics that make them acceptable from an environmental standpoint (low toxicity and eventual degrading into non-toxic components) render them less effective in long term termite control.
One of the most common termiticides, and the only one available to consumers who are not licensed pest control operators, is chlorpyrifos, an organophosphate that is available in emulsifiable concentrate, dust, flowable, pellet, spray, granular and wettable powder formulations. The chemical adsorbs well to soil particles, is not readily soluble in water, and has a half life of 2 weeks to a year, but most commonly 60 to 120 days. Chlorpyrifos acts as a cholinesterase inhibitor, interfering with the proper working of the nervous system. It works as a contact poison, but also as a stomach poison. A conventional termite barrier laid down by spraying chlorpyrifos is expected to kill termites that pass through it, and to generate secondary kills in the nest when the carcasses of poisoned termites are carried to the nest and cannibalized. The half life virtually assures that the efficacy of the chemical will end before that of the structure.
To enhance the effectiveness of termiticidal compounds, both before and after the banning of chlorinated hydrocarbons, the chemicals were combined into termite "baits" consisting of the poison and an attractive termite food, namely, some form of cellulose. The objective is to induce the termites to ingest the poisoned food and return with it to the nest, where food is normally regurgitated and shared with the rest of the colony. Two early examples are U.S. Pat. No. 3,858,346 (Bailey) and U.S. Pat. No. 4,582,901 (Prestwich). Bailey disclosed impregnation of building timbers with hexachlorocyclopentadiene dimer in an organic solvent such as benzene or carbon tetrachloride as the termiticide, and also spreading bait comprising the same poison added to a termite-attracting carbohydrate carrier such as citrus pulp, sawdust and decaying wood. Prestwich discloses modifying the chemical composition of cellulose to include fluorinated ester moieties. The modified cellulose may be formed into bait blocks or injectable dust for placement in areas to be protected or treated.
In more recent, environmentally safer approaches, U.S. Pat. No. 5,564,222 (Brody) discloses impregnating cellulose items, such as wc , oden or cardboard stakes, balls or pellets with a wa t soluble borate salt. The termites are attracted to and consume the cellulose and the borate salt functions as a slow-acting termiticide. U.S. Pat. No. 5,573,760 (Thorne, et al.) discloses using a termite monitor in the form of a perforated cartridge containing a cellulose-rich composition, water and an exogenous nitrogen source. Once foraging termites encounter the desirable food source, they recruit others, and a tunnel to the device is constructed. This allows early detection of termites near a protected structure, as the bait is a more desirable food than the structure. Once activity is identified, the cartridge can be removed and replaced with a similar cartridge containing the same food composition, but laced with a slow-acting termiticide.
The bait approach as previously implemented has at least two disadvantages. First, there are necessarily gaps between the bait modules, leaving the possibility that termites may simply miss the bait, tunneling between the modules and reaching and infesting the protected structure. Current protection standards require a horizontal barrier and vertical curtain without any gaps. Second, placing of the bait modules, whether spikes, buried balls, pellets or dust, is time consuming, labor intensive and consequently expensive. The closer together the bait modules, the more work and expense involved.
Thus, it is an object of the invention to provide a termite control mixture that includes a poison mixed with a food source that may be, applied uniformly across an area of property. It is a further object to provide a mixture of termiticide and food that may be applied using the same equipment and techniques employed by pest control operators to administer standard termiticidal compounds. It is a further object to distribute the mixture in the ground to form a continuous barrier between subterranean termites and the structure to be protected. It is another object to enhance the effectiveness of a given amount of poison by inducing termites to ingest poisoned food and return with it to the nest, poisoning other termites and the queen. It is yet another object of the invention to afford termite protection and control using a smaller amount of potentially harmful poison than is necessary with standard termiticides.